The present invention relates to a laminar textile construction material, particularly suitable for acoustical components.
The textile construction according to the present invention may be used in all electronic devices, made either in a small or large series, including at least an audio function, such as a sound emission, either of a vocal or musical type, by loudspeakers or similar devices, or a sound reception by microphones of any desired types.
To the above mentioned broad electronic apparatus group pertain several products, such as the following most common devices: land and cellular phones, free hand devices and other fittings, Skype and SAT phones, walkie-talkies, audio devices built-in in helmets and the like, professional radio apparatus for military, safety and civil protection applications and outdoors works; hand-held Hi-Fi systems, such as MP3 read-out devices, earpieces, headphones, hand-held acoustical boxes, professional audio devices such as microphone and headphones, loudspeaker components; TVs, monitors, hand-held DVD players and the like; satellitar navigators including vocal signaling capabilities; car Hi-Fi systems, vocal warning systems; indoor communication devices for trains, airplanes, ships; loudspeakers for computers and audio fittings in general; domestic application fittings such as entryphones, indoors audio communication devices; acoustic devices for hard of hearing people and other sanitary apparatus.
As further known, in a number of hand-held systems, such as cellular phones or walkie-talkies, these devices are also designed, in most cases, for outdoors applications, and not only for closed environment uses.
Thus, for these devices, and for all products to be used outdoors, a protection from atmospheric agents is a very important issue.
In particular, such a protection would be necessary on inner acoustic components, such as loudspeakers and microphones.
In fact, the above components are very delicate ones, and must be protected from intrusion of water and solid particles such as powder, dirt, dangerous debris, without causing the sound emitting or receiving characteristics, as originally designed, to drop.
Thus, the functional requirements for the above mentioned acoustic components are rather complex, since they must combine good sound transmission characteristics, to be achieved by large openings formed through the device outer shell, with a satisfactory protection of the device component, which protection would require to insulate as far as possible the acoustic component from the outside environment.
The most commonly used protective system provides to apply porous protection arrangements on the outer openings or ports, which, in a typical cellular phone, are usually three and are arranged through the main loudspeaker, microphone and free hand used/ringtone speaker.
For protecting the above mentioned acoustic components, different approaches are conventionally used, depending on the application requirements and protection degree to be achieved.
In some rare cases, no component protection is used, whereas, in other cases, protecting bars or grids, molded of a plastics material, with an exclusively anti-impact function are used.
Another protective system comprises large mesh protective nets, such as protective metal nets, microphone bulb protecting net arrangements, or plastics material molded grids.
The above protective arrangements also having a protective function against a possible intrusion of small articles, such as pencils and the like.
Yet another protective system comprises a screen made of a non-woven fabric material, with an optional water repellent treatment, arranged in the front of the acoustical component.
Said protective screen may also be made of a technical synthetic single-thread fabric material, processed by an optional water repellent treatment.
Yet another protective system comprises a water repellent expanded PTFE or E-PTFE membrane.
The above disclosed three approaches, however, are not adapted to provide a protection from liquids, but only a limited protecting efficiency against solid articles having from middle to large dimensions, while the other above mentioned protective arrangements assure a good protection even against a possible intrusion into the acoustical component of liquids and powders.
The latter protective arrangements conventionally comprise textile components, usually of a synthetic type, in the form of fabrics, non-woven fabrics or membrane materials.
For an easy assembly to protect the acoustical components, the textile material must have a suitable form or shape; in this respect, different assembling solutions would be possible, depending on the configuration and size of the end product.
In most common cases, such as in cellular phones, the protective textile material screens are assembled together with gasket elements made of synthetic foamed materials and bi-adhesive tape templates, assuring a full adhesion of the protective screen to the outer body of the device being protected.
The above components are usually made of a technical polyester single-thread fabric material, and comprise an annular gasket element provided with an adhesive area to be glued on the cellular phone shell.
From an acoustical standpoint, the protective screen, as provided, must not alter the inlet and outlet sound flow, with respect to the designed parameters.
Usually, for a main part of large consume acoustic products, it is necessary to minimize the sound pressure level attenuation or dropout.
Thus, the protective screen must be an acoustically transparent one, and should provide its protective function while interfering as less as possible with the acoustic component inlet or outlet sound flow, which event is very common for cellular phones, in which the protective screen does not excessively attenuate the cellular phone loudspeaker sound or microphone sensitivity, to allow small, light and inexpensive acoustic members to be used.
In other cases, frequently related to from middle to high range acoustic products, the protective screen should provide a true acoustic function, so as to level possible emission peaks or distorted sounds, to differently balance the frequency response of the acoustic component.
Such a feature would be a particularly interesting one for low frequencies, which are rather critical in small loudspeakers, and which may be amplified by introducing a textile material section on the back portion of the loudspeaker, as it occurs in some earpieces.
In all cases it can be said that the textile material component, made of a fabric, non-woven fabric or membrane material, must preserve the originally designed acoustical characteristics precise which, depending on the target application, may vary from a maximum acoustic transparency to a set sound attenuation level.
To precisely define and set the above acoustic characteristics, several systems and methods may be used.
One of said systems comprises a measurement of a specific resistance to the passage of air (ASTM C522-87), relating the flow rate to the load loss for a stationary air flow passing through the textile product.
The results are expressed in Rayls MKS and to low values of this parameter will correspond, as well known, acoustically transparent materials.
Another system provides to perform a measurement of an acoustic impedance value, based on the same above parameters, but measured for an air flow alternating regimen, that is under conditions more adherent to the acoustic application actual properties.
According to yet another system, it is possible to directly test the acoustical screen in an as constructed configuration thereof, that is with a shape and size identical to the assembled commercial product shape and size, thereby performing a direct measurement of the sound pressure level, either with or without a textile screen arranged between the sound source and measurement microphone.
The test result is usually expressed in decibels, dB (SPL), and depends on different standardized measurement methods (ISO/FDIS 7235:2003 or the like).
The latter measurement system is the most interesting one and has been used for testing acoustic components having a size similar to that of the most critical cellular phone components, that is disc elements of a diameter of 3-5 mm built-in in the phone microphones.
Loudspeakers, on the other hand, require less acoustically critical double or triple dimensions.
Owing to a specifically designed configuration of the test sample and holder therefore, very similar to a real application, samples of the above mentioned type have been subjected to direct acoustical measurements, with the following results:
A reduction to about −1.5 dB (SPL) would be normally acceptable in the phone field and would correspond to components with a limited acoustical attenuation, or even “acoustically transparent” components.
Higher losses, of a value up to −15 dB (SPL), would be yet acceptable if a perfect sound would not be required and if it would be possible to offset the performance balance in favour of protective properties, (to the detriment of a perfect acoustic performance), such as, for example, in heavy duty walkie-talkie devices, waterproof cellular phones, military radio sets, and other applications in which it is necessary to transfer a simple vocal and not a true musical signal.
The International Standard IEC60529 defines the “Ingress Protection” index with reference to some much or less hard test conditions, in which the electronic component shell is subjected to an intrusion of either solid articles or water.
The first digit of the above IP index is related to the solid material intrusion resistance. Index levels from IP1X to IP4X would be usually of low interest for acoustic components which, on the contrary, nearly always require an IP5X level, assuring a partial protection against a powder intrusion.
An IP6X level requirement, related to a perfectly sealed or tight component, is, on the contrary, less common.
The second digit of the above IP index is related to the water resistance.
Thus the IPX3, IPX4 and IPX5 levels are related to-different intensity water sprays.
Usually, for the most common products or articles, such as cellular phones, a IPX3 level would be just sufficient.
On the contrary, the “heavy duty” acoustic product market requires a protection level up to IPX7, corresponding to an immersion into a water pool to a depth of 1 meter for 30 minutes.
It should be apparent that the above are very stringent conditions, which, at present, are met only by a textile material, that is the E-PTFE water-repellant membrane.
However, protective screens made of a technical fabric material have improved performances with respect to the protection of acoustic components from water and solid particles.
To better understand the above, it is possible to resume the provided observations into only two classes, therein are included the most part of protective screen including acoustic devices: the IP53 (or IP54) and IP67 level.
More specifically, the IP53 (or IP54) level is required in a most part of cellular phones and handheld audio devices.
In fact, in addition to a sufficient powder protection, the above products require a satisfactory protection from rain water and other liquid spray intrusion.
Protection levels up to IP54, related to middle pressure water jets, are generally considered as sufficient in the cellular phone market, in which a valid protection from rain and water sprays is desired, but in which an impermeable product capable of resisting to immersion to a set depth into water is not truly required.
The IP67 level, more stringent than the preceding one, provides that the product is adapted to resist to a water immersion up to a depth of 1 meter for 30 minutes.
It should be apparent that the above requirements must be met only for very is stringent heavy duty applications, such as military radio sets, walkie-talkies used in outdoor yards and work areas, police and safety communication devices, sea applications and the like.
As above disclosed, the main part of consume acoustical products, such as cellular phones, generally require an IP53 or IP54 protection level.
However, to the above it should be further added that, even for the latter products, a recent designing trend is to provide a higher protection level, up to IP67, to allow these devices to be perfectly protected from accidental water intrusions.
Accordingly, at present, a protecting IP67 index level is used even for products which previously did not require it.
Thus, the textile components for protecting acoustic members or components will be further correspondingly improved in a near future.
Moreover, as above disclosed, at present three different technical solutions are adopted, based on different textile products, adapted to provide the acoustical and protection performance required by modern acoustic products, that is the non-woven fabric materials, the synthetic single thread technical fabric materials and water repellent E-PTFE membranes.
The multi-thread fabric materials, because of their uneven nature, are rarely used and have characteristics similar to those of the non-woven fabric material.
Between the above mentioned textile products, said non-woven fabric materials have a less acoustic applications performance.
They generally provide a protection level corresponding to IP53 or IP54, but are not suitable to resist against long duration water immersions.
The water intrusion pressure values vary from 15 to 30 cm water column (1500-3000 Pa), and are not sufficient to provide an IP67 protection level.
From an acoustical standpoint, the above materials cannot be considered as perfectly suitable or valid.
In fact, they may achieve acoustical impedance values corresponding to 50-60 Rayls MKS, but may not descend under such a limit, thereby they are not a perfectly transparent acoustical filter.
Specifically designed tests, carried out on components similar to that used in a real application (cellular phones) have demonstrated that this type of material shows a sound pressure level reduction of the order of 3-5 dB(SL), which value is not a low value and moreover it is not easily repeatable.
In actual practice, in the acoustical field, non-woven fabric materials do not represent the best choice, since they are outclassed both by the single thread fabrics (with respect to the acoustical characteristic) and by the membranes (with respect to the water repellent properties).
The technical synthetic single thread fabrics, in turn, have an open square mesh construction allowing to minimize the air passage resistance.
They provide an optimum acoustical performance: their acoustical impedance usually varies in a range from 5 to 300 MKS Rayls, and may also arrive at 2000 Rayls for some special products, and the sound pressure level reduction is in a range of 0.1-2.0 dB (SPL), which is absolutely the best performance of all the textile components used in acoustical products.
FIG. 8 shows a frequency response of a fabric material having an acoustical impedance of 90 MKS Rayls, which corresponds to about a middle point of the above disclosed range, and showing an average or middle sound pressure level loss of 0.7 decibels, in a typical cellular phone application.
On the contrary, because of their comparatively high free surface rate, the open mesh fabrics are not suitable to provide optimum water repellent characteristics.
Normally, the components made of these fabrics provide a protecting index corresponding to IP53 or IP54 and, in this respect, are rather similar to non-woven fabric materials (with a resistance up to 20 cm of water column).
Such a protection level, on the other hand, is suitable for a very large number of applications, such as a lot of cellular phone field products, but does not meet the protection requirements of the above mentioned heavy duty applications.
Accordingly, the present development target of the single thread acoustical fabrics is that of achieving an improved or greater protection index, up to IP67 or IP68, in order to correspondingly increase possible practical application ranges, including even those having most stringent requirements with respect to the water resistance standpoint.
The E-PTFE impermeable membranes, also used in the acoustical field, provide an optimum protection against liquid intrusion.
Intrusion pressure values near to or greater than 10 meters of water column (=1 bar) allow the E-PTFE membranes to achieve protection levels corresponding to at least IP67, or even to IP68, thereby providing these materials with optimum water repellent properties.
On the contrary, the acoustical performance of said E-PTFE membranes is not optimum.
In fact, they conduct sounds mainly by a vibration effect, involving a comparatively high reduction of the sound pressure level, usually near to −10 dB (SPL) for a typical size of acoustic components.
A further drawback of the above mentioned membrane is their extremely variable frequency response.
As shown in FIG. 9 diagram, a typical membrane may loss about 10 dB at low frequencies and only 1-2 dB at higher frequencies: accordingly, the transmitted sound quality is partially deteriorated.
To conclude, among the above mentioned three textile products conventionally used in the acoustical field, the E-PTFE membranes are those having a lower acoustic performance.
On the other hand, it should be pointed out that in heavy duty acoustic applications, it is usually necessary to transmit human voice only and not music: accordingly, a non optimum sound quality may be tolerated.
However, this is a gap or defect of currently available products, thereby it would be desirable to provide an improved product at least assuring a more constant or flat frequency response and a more predictable performance, while preserving the required impermeable characteristics.
Finally, to the above it should be further added that the mentioned E-PTFE membranes also have the following defects:
a small mechanical strength and a high damage sensitivity;
a difficult die-cut and assembling process since the cold cutting operation does not provide an optimum quality, and is necessary a great industrial process set-up with consequent problems in inlet strip splicings;
a high elasticity, negatively affecting a proper coupling with other materials and providing variable stresses in the finished article, with a poor repeatability of the acoustic characteristics;
non perfectly constant dimensional parameters, particularly the membrane thickness;
an impossibility of making from middle to large dimension or size components;
the requirement of adding a protective film to the membrane half-processed product, with an additional expense;
the requirement of using much more expensive adhesive materials, specifically designed for PTFE.
Thus, none of the above mentioned currently used materials allows to fully meet the market requirements, in particular if an IP67 protection index is required.
Thus, it would be desirable to provide a novel product for the above mentioned applications which has impermeable properties as good as those of the membranes, while allowing to overcome all the defects of the latter, with respect to the acoustic lack of coherence, and to their poor mechanical characteristics.